From a141b5264109f133ba244514e382514cb313295e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Ol=C5=A1=C3=A1k?= <marek.olsak@amd.com>
Date: Mon, 20 Nov 2023 05:41:31 -0500
Subject: [PATCH] st/mesa: disable light_twoside if back faces are culled
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This potentially improves performance.

Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26308>
---
 src/mesa/state_tracker/st_atom_rasterizer.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/mesa/state_tracker/st_atom_rasterizer.c b/src/mesa/state_tracker/st_atom_rasterizer.c
index f76991e2d75..160860d4463 100644
--- a/src/mesa/state_tracker/st_atom_rasterizer.c
+++ b/src/mesa/state_tracker/st_atom_rasterizer.c
@@ -295,6 +295,10 @@ st_update_rasterizer(struct st_context *st)
          raster->cull_face |= PIPE_FACE_BACK;
    }
 
+   /* Disable two-sided colors if back faces are culled. */
+   if (raster->cull_face & PIPE_FACE_BACK)
+      raster->light_twoside = 0;
+
    /* _NEW_TRANSFORM */
    raster->depth_clip_near = !ctx->Transform.DepthClampNear;
    raster->depth_clip_far = !ctx->Transform.DepthClampFar;